[ 43 ] 



III. On the Morphology of a Beptilian Bird, Opisthocomus cristatus. 

 By W. K. Paeker, F.B.S. 



Received January 4th, 1890, read February 4th, 1890. 



[Plates VII.-X.] 



Contents. 



Page 

 I. Introductory Eemarks on the Present Existence of Birds closely related 



to Reptiles 44 



II. The Early Stages of Opisthocomus cristatus 48 



III. The Skull of Opisthocomus cristatus in Embryos and Adult 49 



IV. The Vertebral Chain of Opisthocomus cristatus 59 



V. The Sternum and Shoulder-girdle of Opisthocomus cristatus 64 



VI. The Wings of Opisthocomus cristatus 69 



VII. The Hip-girdle of Opisthocomus cristatus 74 



VIII. The Hind Limb of Opisthocomus cristatus 77 



IX. Recapitulation and Summary. 



a. The Ornithological Position of Opisthocomus 80 



6. The Light cast upon the Ontogeny of Birds by the Morphology of 



Opisthocomus 81 



X. List of Abbreviations 83 



XI. Description of the Plates 84 



xLARLY last year Mr. Sclater received from Mr. John J. Quelch, C.M.Z.S., of the 

 Museum, Georgetown, British Guiana, a series of embryos of the Hoatzin [O^istlio- 

 comus cristatus). Some of these, after due examination by Mr. F. E, Beddard ^, were 

 sent to me by Mr. Sclater. My study of the adult has been from the two skeletons in 

 the Museum of the Eoyal College of Surgeons, kindly lent me by the President, 

 Sir W. Savory, and the Curator, Prof. Charles Stewart. I take this opportunity of 

 thanking all these friends for their kindness. 



Hitherto my knowledge of the structure of the skeleton of this bird has been 

 derived from Prof. Huxley's masterly description, given partly in his paper " On the 

 Classification of Birds," and more completely in his paper " On the Classification and 

 Distribution of the Alectoromorphse and Heteromorphas " (Proc. Zool. Soc. 1867, 

 pp. 415-472; and ibid. 1868, pp. 294-319). 



' See Mr. Beddard's paper, ' Ibis,' 1889, p. 283. 



VOL. xin. — PAET II. No. 1. — A;pril, 1891. H 



